With the attacks preventing thousands more from voting even after their identities had been verified by the shadow elections commission, organizers decided to extend the two days of voting into a third day Monday.

“We plan to end the voting at 8 p.m. tomorrow and announce preliminary results at 9 to 10 p.m.,” opposition leader Sergei Udaltsov said Sunday.

The 59,054 ballots cast by Sunday night represented more than a third of the 169,866 people who had registered to vote, said Leonid Volkov, head of the elections commission. But many more were eligible after his commission had verified the identities of 95,717 people by late Sunday.

The political opposition, facing a leadership vacuum following months of sporadic and sometimes disjointed protests, called the weekend election to select a 45-member leadership body called a coordination council. Among the more than 200 candidates in the running were familiar faces like Udaltsov, anti-corruption blogger Alexei Navalny, environmentalist Yevgenia Chirikova and socialite Ksenia Sobchak.

On Saturday and Sunday, hundreds of people lined up at tents serving as polling stations on Trubnaya Ploshchad to have their passports checked and to cast their votes on the election commission’s website, cvk2012.org. People also could vote from home by submitting a photo of themselves with their passports or paying a token 10-ruble fee online, which organizers said would deter falsifications.

But DDOS attacks prevented people from voting for much of the day Saturday and continued to interfere with the voting process on Sunday, organizers said. Instead of offering an opportunity to vote, the website carried an announcement that its server was facing problems and voters should try again later.

Udaltsov and other people on Trubnaya Ploshchad blamed the attack on Kremlin forces and interpreted it as a sign that the authorities were afraid of the opposition.

“There’s no doubt that the special services are standing behind this attack,” opposition leader Garry Kasparov, a council candidate, told reporters Sunday. “But our team of professionals, headed by Leonid Volkov, is dealing with the attack, even though it’s very difficult.”

The attack took Volkov by surprise. He had told reporters last Tuesday that he didn’t expect serious problems with voting and noted that measures had been taken to protect the server against attacks.

“This was no ordinary DDOS attack but a special one that could invade our website’s system,” Volkov, speaking about Saturday’s trouble, said in an interview late Sunday.

He accused fringe groups that he said were connected to the Kremlin, including a neo-Nazi group headed by Maxim Martsinkevich, of being behind the attacks. He said Martsinkevich supporters had wanted to be registered as candidates but had been rejected by his commission.

After being offline for most of the day, the elections website came back online Saturday evening, Volkov said. But after 20 minutes during which more than 600 people voted, the server crashed again. The voting again was restored at midnight, and 8,500 people voted until 8 a.m. Sunday, when a new attack occurred.

The new attack, however, was much less fierce, organizers said, and they were able to quickly regain control over the site.

Anti-Kremlin sentiment hung over Trubnaya Ploshchad during the City Hall-authorized gatherings over the weekend. A stage set up for the event carried a banner reading “For our and your freedom.” Four makeshift polling stations saw up to 50 people at a time waiting in line on Saturday, and the numbers swelled considerably Sunday. Other voting booths were set up elsewhere around the city.

Among traditional slogans such as “Russia without Putin,” which could be heard from opposition leaders on the square’s stage, a member of the elections commission, Denis Yudin, appeared on the stage several times Saturday to ask people to get their identities verified even if they couldn’t vote. “It’s important to get verified at this time,” he said.

At the end of the day, he announced that the identities of some 1,000 voters had been verified and that 2,000 to 2,500 people had visited the square. Volkov said fewer people showed up to rally Sunday but more people stood in line to vote.

Yudin rued the possibility that the cyberattack might have cost the votes of retirees. “Of course, we will lose the votes of pensioners who decided to come on Trubnaya Ploshchad only on Saturday and vote,” he said.

Still, Solidarity leader Boris Nemtsov, who is also running for the coordination council, expressed delight that so many people had showed up to vote in person.

“I liked the lines most of all. This is a great success,” Nemtsov said in an interview on the square. “I voted late Friday night,” he added. “I didn’t know about the attack but suspected it might happen.”

Udaltsov, surrounded by a group of admirers shouting, “Take care, we need you” during Saturday’s gathering, said that the authorities were scared of the opposition. “If a protest is legitimized through the [coordination] council, the opposition movement will grow,” he said. “If this doesn’t happen, more people will be in prison, including me and Navalny.”

He noted that the next anti-Kremlin March of Millions would be held in December. On Sunday, he announced that the opposition would rally at Dubrovka Theater at 10 p.m. on Oct. 26 to remember the 10th anniversary of a terrorist raid there that left 129 people dead.

Opposition supporters said in interviews on the square that they were voting for the best-known opposition leaders.

Lyudmila, a 69-year-old pensioner who declined to give her surname, citing fear of being pursued by the authorities, said she supported candidates from the Civil Platform bloc, whose members include liberal journalists Filipp Dzyadko and Sergei Parkhomenko, poet Dmitry Bykov and Sobchak.

Alyona Artasheva, 22, a journalism student, said that even though she supported left-leaning activists like Udaltsov, the most important thing was that all future council members find a common language to make solid decisions. “I hope the council will help this to happen,” she said.

Dmitry Sokolov, a 39-year-old procurement manager, said his vote would go to liberal leaders, but he liked the idea of allowing various viewpoints to be represented on the council. “Nationalism is pretty popular in our society,” he said. “It would be better if they were part of the council — a more or less legal organization — than to be left organizing their own activities.”

He added that he had decided to come to the square to vote because “online voting seemed unclear and long.”

An elderly husband and wife said they have become a fixture at opposition events because they were tired of “lies” and “unfair elections.”

“We want to see what fair elections are like and support liberal activists, particularly Alexei Navalny,” said Ivan Rakovsky, 63, as his wife, Antonina, 60, nodded in agreement.